Field of Invention
This application concerns a procedure or method to produce a circular bore for a fastener or the like in laminated or layered sheet material which is first pierced to form an opening and subsequently bent in a shaping operation, the bending causing a relative shift between layers and distortion of the opening.
In the automobile industry, there has been a relatively recent recognition of the advantages in using laminated sheet material for various parts of the vehicle. For example, laminated or layered sheet material can be used for parts such as an engine oil pan to produce desirable noise dampening properties. Other potential applications include valve covers, air cleaner housings and various covers or shields.
Openings are formed in the above mentioned parts during a blanking operation in which a desired pre-bent shape is struck out from flat sheet material. Conveniently, the openings are formed at the same time. Subsequently, the flat part is shaped into a desired configuration by bending of the sheet material. When laminated or layered materials are bent, the layers are shifted relative to one another. With a simple straight bend, the shifting is in a direction substantially normal to the bend. If a circular opening is first formed in the laminated material, subsequent bending will shift the layers and produce a non-circular opening. If the layers are shifted enough, the resultant opening in the material could disappear.
Therefore, it is desirable to form openings in flat laminated sheet material which are so configured so that after a bend is made, a circular opening is produced in spite of shifting between the layers.
A search was conducted on this procedure and the following prior references were uncovered. Although it is not believed that any of the following patents are particularly relevant either taken alone or in combination, they are the closest prior art known to applicant.
The U.S. Pat. No. 2,751,664 to Arnit discloses a nonlaminated sheet material product which starts with an irregular opening and bends the material in two closely spaced bends to trap a ball between the material in the opening.
The U.S. Pat. Nos. 3,006,443 and 3,158,045 to Siler disclose layered structures with offset bores and eccentric special fasteners therefore.
The U.S. Pat. No. 3,580,040 to Lang discloses tooling for forming openings in non-laminated sheet material.
The U.S. Pat. No. 3,238,909 discloses an optical system to correct distortions using pre-printed copy on flat stock. The U.S. Pat. No. 4,577,888 discloses a seat belt anchor formed from two overlying straps (see FIGS. 7 and 8). One of the straps has oblong shaped openings therethrough.